176 NOTES AND COMMENT spawning had occurred in July and August, ovogenesis and growth of ovocytes began immediately and proceeded rapidly through October and November and into December. Proliferation of the follicles through the connective tissue of the visceral mass occurs at this time. Thus, animals collected in January have initiated or may already have completed the development of many of the gametes that would normally be spawned the following August. In Southampton Water, the condition (per cent flesh content) of clams declines more or less continuously following spawn- ing and any renewed gametogenesis and growth of gametes in the autumn can only be occurring at the expense of stored food reserves. The proliferation and major growth of the gonad does not occur until the fol- lowing spring. Thus, animals collected in Southampton Water in January (as were those in experiment 2) have still to under- go the main period of gonad proliferation and may be expected, after conditioning at this time, to release fewer eggs than Long Island Sound clams collected in Jan- uary, or Southampton Water clams collected in June after the spring increase in condi- tion has occurred (as were those in experi- ment 1). These results are important in indicating the dependence of egg production on plank- ton abundance over the clam beds at some time previous to the spawning season. In Long Island Sound this may be the previ- ous autumn, in Southampton Water the previous spring. To what extent the num- ber of eggs produced also depends on con- ditions existing during the 2-2.5 months over which spawning may take place is not known, nor is it known whether in fact new ovocytes are produced and matured during this period to be spawned along with those that developed earlier. If this is the case, then the total egg production of clams in nature could considerably exceed the fig- ures given here and by Davis and Chanley ( 1956 ) , especially at sites where conditions remain suitable for ovocyte production and maturation for an extended period during the summer months. ALAN D. ANSELL~ Department of Zoology and Plankton Laboratory, University of Southampton, England. REFERENCES ANSIZL, A. D. 1963. Venus mercenariu L. in Southampton Water. Ecology, 44 : 396-397. -, F. A. LOOSMORE, AND K. F. LANDER. 1964. Studies on the hard-shell clam, Venus mercenaria, in British waters II. Seasonal cycle in condition and biochemical composi- tion. J. Appl. Ecol., 1: 83-95. DAVIS, H. C., AND P. E. CHANLEY. 1956. Spawn- ing and egg production of oysters and clams. Biol. Bull., 110: 117-128. HEPPELL, D. 1961. The naturalisation in Europe of the quahog, Mercenaria mercenaria ( L ). J. Conch., 25: 21-34. LOOSANOFF, V. L. 1937. Seasonal gonadal changes of adult clams, Venus mercenaria (L.). Biol. Bull., 72: 406416. -, AND H. C. DAVIS. 1950. Conditioning V. mercenaria for spawning in winter and breeding its larvae in the laboratory. Biol. Bull., 98: 60-65. l Present address: The Marine Station, Millport, Isle of Cumbrae, Scotland. PREPARATION OF ARTIFICIAL SEAWATER~ During some physicochemical studies of natural seawater to minimize biological ef- seawater, we used artificial rather than fects and to provide a reproducible solution of known composition. Little attention has l This work was supported by National Science Foundation Grants GP-3582 and GA-301. We been given to the technique for preparing would like to express our appreciation to Drs. P. artificial seawater. We have developed a K. Weyl and K. S. Deffeyes for their suggestions method that gives reproducible and satis- and encouragement during this work. We are factory results. We also have revised the grateful for the suggestions of Mr. K. L. Russell. composition of artificial seawater to agree
NOTES AND COMMENT I77 TABLE 1. Comparison of the composition of TABLE 2. Formula for 1 kg of 35.00% artificial natural and artificial seawaters seawater Ion For- mula wt* Arti- Artificial Natural % ficial seawater? seawater$ differ- sea- (g/kg) (g/kg) enceg water11 (g/kg) A. Gravimetric salts Salt Molecular wt G/kg of solution Cl- 35.453 19.353 19.353 0.0 19.353 Na’ 22.9898 10.764 10.76 0.0 10.765 sot- 96.06 2.701 2.712 -0.4 2.711 Mg” 24.312 1.297 1.294 +0.2 1.295 Ca*+ 40.08 0.406 0.413 -1.7 0.414 K’ 39.102 0.387 0.387 0.0 0.387 HCOS- 61.01 0.142 0.142 0.0 0.142 Br- 79.91 0.066 0.067 -1.5 0.066 Sr*+ 87.62 0.014 0.008 +75 0.008 H3BOz 61.83 0.026 0.026 0.0 0.026 F- 19.00 0.001 0.001 0.0 0.001 * From Weast ( 1965). ? Salinity 35.00%,, Lyman and Fleming (1940). $ Salinity 35.007&, Culkin ( 1965 ) . 8% difference=(t-$)/$X100. jj Salinity 35.OOy& this work. NaCl 58.44 23.926 Na2S04 142.04 4.008 KC1 74.56 0.677 NaHC03 84.00 0.196 KBr 119.01 0.098 &BO, 61.83 0.026 NaF 41.99 0.003 B. Volumetric salts MS,“r”- y:gtg Stock solution. Salt wt tion Concn . %“d;’ MgC12.6Hz0 203.33 0.05327 1.0 M 1.071 g/ml CaCE*2Hz0 147.03 0.01033 1.0 M 1.085 g/ml SrCL*6Hz0 266.64 0.00009 0.1 M 1.013 g/ml C. Distilled water to l,OOO.OOO g with recent determinations of the composi- tion of natural seawater, The formula of Lyman and Fleming ( 1940) has been one of the most widely used recipes for artificial seawater (Harvey 1960; Riley and Skirrow 1965). The com- position of artificial seawater prepared by this formula was compared with recent analyses of natural seawater as reviewed by Culkin ( 1965). The mass of each major constituent per kilogram of solution was calculated for artificial seawater of salinity 35.00% using recent values of atomic and molecular weights ( Weast 1965). These masses were compared with those given by Culkin ( 1965, Table I) and are shown in Table 1. If weighings in the preparation of artificial seawater are made to 1 mg of salt/kg of solution, the differences between the artificial seawater recommended by Lyman and Fleming and natural seawater of the same salinity are significant for SOh2-, Mg2+, Ca2+, and Sr2+. Early determinations of the Sr2+ content of seawater indicated a value of 14 mg/kg, but determinations since 1951 give a value of 8 mg/kg (Culkin 1965). This accounts for the discrepancy in the Sr2+ content of artificial seawater. Lyman and Fleming adjusted the early Ca2+ de- terminations for 14 mg/kg of Sr2+ which partially accounts for the low Ca2+ content of artificial seawater. The Lyman and Fleming formula for artificial seawater was revised to bring the composition of artificial seawater to within 1 mg/kg of natural seawater for all the major constituents. The revised formula for salinity 35.00% is given in Table 2. Impurities in the reagent grade salts used in Table 2 do not change the composition of artificial seawater by more than 1 mg/kg for the major constituents. However, im- purities in these salts are important with regard to the minor constituents of sea- water, If reagent grade NaCl contains the maximum POd3- and Fe impurities (Amer- ican Chemical Society 1955), the artificial seawater will contain ten times the average amount of POb3- and four times the normal amount of Fe in natural seawater. Two factors must be considered in pre- paring artificial seawater: the reagents used must be weighable and of known composi- tion (or they must be standardized against primary standards) and the salts must be added so as to avoid precipitation of in- soluble compounds. The following salts were dried and weighed in anhydrous form: NaCl, NaZS04, KCl, KBr, and NaF. NaHC03 and H3B03 were weighed without drying due to un- certainty in the composition of the dried
NOTES AND COMMENT 179 Skirrow [eds.], Chemical oceanography, v. 1. oceanography, v. 1. Academic, London. Academic, London. 712 p. HARVEY, H. W. 1960. The chemistry and fer- SVERDRUP, H. U., M. W. JOHNSON, AND R. H. tihty of seawaters. University Press, Cam- FLEMING. 1942. The oceans. Prentice- bridge. 240 p. Hall, Englewood Cliffs, New Jersey. 1087 p. LYMAN, J., AND R. H. FLEMING. 1940. Composi- WEAST, R. C. [Ed.]. 1965. Handbook of chem- tion of seawater. J. Marine Res., 3: 134-146. istry and physics, 46th edition. Chemical RILEY, J. P., AND G. SKIRROW. 1965. Chemical Rubber Co., Cleveland, Ohio. MIDGET BENTZEL CURRENT SPEED TUBE FOR ECOLOGICAL INVESTIGATIONS~ Field studies on the behavior of juvenile Bentzel current speed tube that can be chinook salmon and steelhead conducted used wholly submerged (Fig. 1). The by the Idaho Cooperative Fishery Unit have original Bentzel tube described by Welch resulted in development of a miniaturized (1948) is 1.3 m long, weighs about 2 kg, l I thank Mr. David A. Ward, Hydrologic Lab- and is designed to measure velocities rang- oratory, Washington State University, who helped ing from 0.1-1.2 m/set in depths of 0.8 m secure suitable components for construction of or less. This instrument consists basically these devices. of a U-shaped metal tube which has the FIG. 1. Set of three midget Bentzel current speed tubes capable of measuring speeds from 0.1 to 1.2 m/set.